Most people can relate to brake problems because they can appreciate the need to stop in normal riding. Add the occasional crisis and the rider will start thinking about stopping. Suspension, on the other hand, is a vague, theoretical concept that means little to the average rider. Even if they are aware they generally dismiss the bike's forks and shocks as an expensive part of the bike that rarely fails. Unfortunately, it also rarely works very well in stock form. Add miles and neglect and it goes from bad to worse.
While I had the NX's brake caliper off I decided to replace the fork seals. What I found was probably fork oil that might have been changed once since it was built in 1989. Twenty years of sludge were lurking in the bottom of the fork tubes.
Fork tubes are a pretty sophisticated mechanisms that work to keep the tire in contact with the road. Bumps, pot holes, and irregularities are all dealt with in an attempt to balance control with comfort. A fork tube is composed of two linear bearings that allow the wheel to travel up and down. The internal passages and valves open and close to control the flow of fork oil which controls the dampening. This keeps the bike firmly in contact with the road and avoids the oingo-boingo bouncing you see in old Fords with bad shocks. When the oil gets old and filled with sludge the fork can't move the way it's supposed to and traction is lost. The NX was just such a case. Because it happens slowly over time it is hard to appreciate but it is a classic statement that a rider will make, "Boy, it really feels like a new bike!", when the fork oil is replaced. The NX took 420cc per side and used up a 1 liter bottle. Would you pay $15 for a new bike feel? Do it once a year and you'll never have to endure the old bike feel.
It's even easier to do than changing the brake fluid and can often be done at the same time. Most forks have a drain plug at the bottom of each fork leg. Simply unscrew the top fork cap to let air in and then remove the drain plug. Have the drain pan positioned so that it will catch a stream shooting out or you'll have a mess to clean up. When it's all drained out I usually shoot some contact cleaner down the tube to flush out the sludge. Then replace the drain plug and refill the tube with whatever the manufacturer recommends. If you think about it stop at your dealer and get new drain plug washers before you start. They are generally copper washers that cost about $1 apiece.
Note: If you have newer cartridge style forks the good news is that they are much better a doing their job by design. The bad news is that they generally require the dealer and special tools to work on. Do it every third year and enjoy the ride.
Tomorrow I'll close this series with my views of the rear suspension.